1. Field of the Invention
The present invention relates generally to an Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) wireless communication system, and in particular, to a data transmission control method for an OFDM-MIMO wireless communication system.
2. Description of the Related Art
A MIMO technique, which is technology for transmitting/receiving data using a plurality of transmission antennas and a plurality of reception antennas, can contribute to an epochal improvement in system capacity owing to a plurality of independent spatial channels formed by the plurality of transmission/reception antennas. For these reasons, the MIMO technique is well known as a transmission technique suitable for the next generation wireless communication in which high-speed high-capacity data transmission is required. It is well known that in a rich scattering wireless channel environment, approximate capacity of a MIMO Rayleigh fading channel linearly increases with the smaller one among a number of transmission antennas and a number of reception antennas.
OFDM is a transmission scheme for dividing one broadband channel into a plurality of narrowband channels, allocating orthogonal frequencies to the channels, and transmitting different data on the channels. Thus, the OFDM scheme is suitable for high-speed data transmission. In the OFDM scheme, because symbol duration of each subcarrier increases with the number of subcarriers, it is possible to efficiently reduce inter-symbol interference and simply implement the structure of a receiver. Therefore, it is expected that a MIMO-OFDM system, implemented by combining a MIMO system with the OFDM scheme, will become a standard for the next generation wireless communication system.
The latest research into the MIMO system has mainly focused on maximizing a multiplexing gain or a diversity gain. However, because the optimal multiplexing gain or diversity gain can be subject to change according to the given channel environment, application of a fixed MIMO technique in a time-varying environment does not always guarantee efficient channel utilization.
The existing research on the OFDM system shows that it is possible to improve system performance by appropriately adjusting a bit rate and transmission power at a transmitter. However, this technique is limited only to the OFDM system, and adjusts transmission parameters not in a spatial domain but in a frequency domain.
An adaptive modulation and MIMO coding technique has been proposed as a link adaptation (LA) technique for the MIMO-OFDM system. The adaptive modulation and MIMO coding technique improves channel efficiency by changing transmission parameters, such as a modulation scheme and a coding rate, according to time-varying channel conditions. However, the adaptive modulation and MIMO coding technique has a limitation in that the same transmission parameters are applied in the spatial domain and the frequency domain, and is limited in performance improvement because the same transmission power is allocated to all of the subchannels.